Taking the collinear DW in Fig. 1(a) for example, we illustrate a typical band-to-band
tunneling to realize the high MR state for the P bias configuration due to spin mismatch
between L and R. By tuning the direction of vertical bias, the LAF spin valve can be
switched on or off. The giant MR effect is understood from a general picture of phase transition in Fig. 1(b), seen from model (REF ), that the LAF field drives BLG to be insulating by moving the states with opposite spins in the same layer and the states with the same spin in opposite layers oppositely. The vertical bias induces a full spin polarization by moving the states in the opposite layers oppositely. More crucial for the realization of the entirely electric control of the spin valve effect is that the opposite bias induces the opposite spin polarization. We characterize the MR effect
by a resistance ratio
[1]}, [2]}
\(\rho _{\rm MR}=\frac{R_{\rm AP}-R_{\rm P}}{R_{\rm AP}+R_{\rm P}},\) 
